The invention relates to a distance relay equipment that aims to prevent unwanted operation due to over-reach.
In general, for the measured value of fault impedance in a distance relay, the impedance for the fault point is correctly found for the faulted phase, excluding the load current and fault point resistance etc.
However, as is well known, over-reach or under-reach of the set impedance occurs in respect of the other phases (phases associated with the faulted phase).
Here, xe2x80x9cover-reachxe2x80x9d means that the operating range of a distance relay reaches out of the distance which shows a limit of operation or the range of an impedance.
xe2x80x9cUnder-reachxe2x80x9d means that a distance relay detects an internal fault in the operating range of the distance relay, excluding the output of operation.
A typical example of this tendency is the over-reach of the phase of lead in a short-circuit distance relay (ZIS) element described at p252-p254 of xe2x80x9cProtective Relay Techniques, Chapter 3xe2x80x9d published on Apr. 15, 1981 by Tokyo Denki University Publications Office.
Conventionally, as a countermeasure for such over-reach, as described in xe2x80x9cBackup Protective Relay Systemsxe2x80x9d p.41, Volume 37, No. 1, published on Jun. 5, 1981 by Denki Kyodo Kenkyu (Electrical Joint Research), systems of preventing unwanted operation output of a ZIS element of phase of lead during occurrence of a fault, using the operating condition of an over current relay (OCR) shown in FIG. 15, or systems wherein the over-reach zone is restricted by a combination of blinder elements shown in FIG. 16 are widely employed.
In FIGS. 15(a), (b), the OCR combines with a first-stage X1 of a distance relay in ab-phase.
In FIG. 15(b), a circle shows characteristic of an mho relay element that finds a direction of fault, and X1 and X2 paralleling to an R axis shows reactance relay element that finds the distance where fault happens.
Here, in FIG. 15(b), X means xe2x80x9creactancexe2x80x9d, R means xe2x80x9cresistancexe2x80x9d.
Therefore, the operation of over-reach of a distance relay in ab-phase is locked by in-operation of OCR in a phase when a fault happens in bc-phase.
In FIG. 16, the operation of over-reach of a distance relay in ab-phase is locked when Zab is in a blinder operation zone. In FIG. 16, X means xe2x80x9creactancexe2x80x9d, R means xe2x80x9cresistancexe2x80x9d.
Here, xe2x80x9cblinder elementsxe2x80x9d mean discriminating filter to protect the unwanted operation of the distance relay.
However, when the OCR operation condition is employed in combination with a ZIS element, there is the problem that the fault detection current sensitivity of the ZIS element depends on the magnitude of the load current.
Specifically, in the case of a heavy load system, it is necessary to raise the operation sensitivity of the OCR setting to a level such that this is normally not operated.
But, as a result, inevitably, the operation detection sensitivity of the ZIS element when a fault occurs is adversely affected. Namely, distinguishing the fault is adversely affected, making it difficult to distinguish the fault current and load.
Also, in the case of a countermeasure using the blinder element, the cooperation of the setting value such as to exclude the load impedance and setting with the object of preventing over-reach on fault occurrence can be difficult to operate, making it difficult to select an optimum setting value for use.
It is an object of the present invention to provide a distance relay of high reliability by adopting a principal that does not depend on the magnitude of the load current for preventing unwanted operation of a distance relay element due to over-reach.
It is a further object of the present invention to provide a distance relay wherein special consideration of setting in use is unnecessary, and wherein high reliability is provided, unaffected by system conditions.
These objects can be achieved according to this invention by providing, in first aspect, a distance relay equipment for detecting a protective region having a fault, among a protective zone that includes a plurality of protective regions, based on a status of a power system, comprising:
an operation decision unit having short-circuit fault distance relay elements that input respectively an electrical quantity from an AC power system of three phases a, b and c, the operation decision unit calculating a fault impedance from each of the electrical quantity to compare said fault impedance, which correspond to ab-phase, bc-phase and ca-phase, with a set impedance, to produce a judging signal of each ZIS element (ZIS element-ab, ZIS element-bc and ZIS element-ca), depending on said result of said comparison;
a calculating unit for calculating a phase-to-phase voltage amplitudes(|Vab|, |Vbc|, |Vca|) in said ab-phase, bc-phase and ca-phase ;
a minimum phase voltage selection unit for selecting a minimum voltage phase (Vxcex94min) for the phase-to-phase voltage amplitudes(|Vab|, |Vbc|, |Vca|) determined by said calculating unit;
a fault phase element output unit for having an AND function, which is set to each of the phases (ab-phase, bc-phase, ca-phase) of said minimum voltage phase (Vxcex94min) selected by said minimum phase voltage selection unit and said judging signal (ZIS element-ab, ZIS element-bc and ZIS element-ca), and outputs an operation signal, to separate, the protective region having the fault, from the protective zone, of said ZIS element-ab, said ZIS element-bc and said ZIS element-ca, if said AND condition is satisfied; and
an operation output unit for judging whether or not two or more operated phases of the ZIS elements are present, to output an operation signal of said ZIS elements to separate the protective region having the fault from the other protective zones.
In second aspect, there is provided a distance relay equipment according to the first aspect, wherein said minimum phase voltage selection unit comprises:
a first unit for determining a first value equal to the absolute value of the difference between the absolute value of a first phase voltage and the absolute value of a second phase voltage;
a second unit for determining a second value equal to the absolute value of the difference between the absolute value of a first phase voltage and the absolute value of a third phase voltage;
a selection unit for selecting the first phase voltage if
i) the first and second values are greater than a predetermined threshold,
ii) the absolute value of the difference between the absolute value of the third phase voltage and the absolute value of the second phase voltage is less than the predetermined threshold, and
iii) the difference between the absolute value of the third phase voltage and the absolute value of the first phase voltage is greater than the predetermined threshold;
the selection unit selecting the second phase voltage if
i) the first value is greater than the predetermined threshold,
ii) the second value is less than the predetermined threshold, and
iii) the difference between the absolute value of the first phase voltage and the absolute value of the second phase voltage is greater than the predetermined threshold; and
the selection unit selecting the second phase voltage if
i)the first value is less than the predetermined threshold,
ii) the second value is greater than the predetermined threshold, and
iii)the difference between the absolute value of the first phase voltage and the absolute value of the third phase voltage is greater than the predetermined threshold.
In third aspect, there is provided a distance relay equipment according to the second aspect, further comprising:
a third unit for selecting the minimum voltage phase among said first phase voltage, said second phase voltage and said third phase voltage if said selection unit does not select one of the phase voltages.
In fourth aspect, there is provided a distance relay equipment according to the second aspect, wherein said predetermined threshold is about 0.05 pu.
In fifth aspect, there is provided a distance relay equipment according to the first aspect, wherein said operation decision unit outputs a judging signal if the followings equations are satisfied:
(Iabxe2x88x92Vabxc2x7sin xcex8)/I2abxe2x89xa7Xs;
(Ibcxe2x88x92Vbcxc2x7sin xcex8)/I2bcxe2x89xa7Xs; and
(Icaxe2x88x92Vcaxc2x7sin xcex8)/I2caxe2x89xa7Xs;
where Iab, Ibc and Ica are a phase-to-phase current;
where Vab, Vbc and Vca are a phase-to-phase voltage; and
where Xs is a setting impedance.
In sixth aspect, there is provided a distance relay equipment according to the first aspect, wherein said operation decision unit outputs a judging signal if the followings equations are satisfied;
Xsxc2x7Iabxe2x88x92Vabxc2x7Iabxc2x7sin xcex8xe2x89xa70;
Xsxc2x7Ibcxe2x88x92Vbcxc2x7Ibcxc2x7sin xcex8xe2x89xa70; and
Xsxc2x7Icaxe2x88x92Vcaxc2x7Icaxc2x7sin xcex8xe2x89xa70;
where Iab, Ibc and Ica are a phase-to-phase current;
where Vab, Vbc and Vca are a phase-to-phase voltage; and
where Xs is a setting impedance.
In seventh aspect, there is provided a distance relay for detecting a protective region having a fault, among a protective zone that includes a plurality of protective regions, based on status of a power system, comprising:
an operation decision unit having ground fault distance relay elements that input respectively an electrical quantity from an AC power system of three phases a, b and c, calculating a fault impedance from each electrical quantity and compare said fault impedance with a set impedance and that, making a judging signal of each ZIG element (ZIG element-a, ZIG element-b and ZIG element-c), depending on said result of said comparison;
a calculating unit having an under-voltage relay element, outputting a judging signal if an absolute value of each phase voltage (|Va|, |Vb|, |Vc|) is larger than a prefixed value;
an output unit identifying whether or not said judging signal outputted from said calculating unit is present for two or more phases;
a final output unit, if said judging signal is present for two or more phases in said output unit, performing an output of an operation signal, to separate a protective region having fault from the protective zone, of all of said judging signal of said operation decision unit to a non-operated side.
In eighth aspect, there is provided a distance relay equipment according to the seventh aspect, wherein said calculating unit includes an mho relay element.
In ninth aspect, there is provided a distance relay equipment according to the seventh aspect, wherein said calculating unit uses the following equations of said mho relay element:
Msxc2x7Iaxc2x7Vpaxc2x7cos xcex8xe2x88x92Vb2 greater than 0;
Msxc2x7Ibxc2x7Vpbxc2x7cos xcex8xe2x88x92Vc2 greater than 0;
Msxc2x7Icxc2x7Vpcxc2x7cos xcex8xe2x88x92Va2 greater than 0;
where Ms is a setting value of an mho element;
where Ia, Ib and Ic are a phase current; and
where Vp is a polarity voltage.
In tenth aspect, there is provided a distance relay equipment according to the ninth aspect, wherein said operation decision unit outputs a judging signal if the followings equations are satisfied:
(Iaxc2x7Vaxc2x7sin xcex8)/I2axe2x89xa6Xs;
(Ibxc2x7Vbxc2x7sin xcex8)/I2bxe2x89xa7Xs; and
(Icxc2x7Vcxc2x7sin xcex8)/I2cxe2x89xa7Xs;
where Ia, Ib and Ic are a phase current;
where Va, Vb and Vc are a phase voltage; and
where Xs is a setting impedance.
In eleventh aspect, there is provided a distance relay equipment according to the ninth aspect, wherein said operation decision unit outputs a judging signal if the followings equations are satisfied:
Xsxc2x7Iaxe2x88x92Vaxc2x7Iaxc2x7sin xcex8xe2x89xa70;
Xsxc2x7Ibxe2x88x92Vbxc2x7Ibxc2x7sin xcex8xe2x89xa70; and
Xsxc2x7Icxe2x88x92Vcxc2x7Icxc2x7sin xcex8xe2x89xa70;
where Ia, Ib and Ic are a phase current;
where Va, Vb and Vc are a phase voltage; and
where Xs is a setting impedance.
Another invention consists of a digital distance relay having a first-stage immediate-operation zone short-circuit distance relay element that inputs respectively the voltage and current from an AC power system of three phases a, b and c, calculates a fault impedance from these voltages and currents and compares this with a set impedance and that, depending on the result of this comparison, makes an operation decision in the event of a fault within a transmission line protection zone, comprising: a first means for calculating the amplitudes |Vab|, |Vbc|, and |Vca| of the line-to-line voltages of the three phases; a second means for making a comparison decision of the absolute value (|Vxcex94|=||Vab|xe2x88x92|Vbc||) (rotated in phase order for the other phases) of the phase-to-phase difference of said voltage amplitudes and a sensitivity constant Vk; a third means for making a comparison decision of the phase-to-phase difference (Vxcex94=|Vab|xe2x88x92|Vbc|) (rotated in phase order for the other phases) of the voltage amplitudes and Vk; a fourth means that deems valid the operation output of the short-circuit distance relay element if the phase for which |Vxcex94| less than Vk in said second means and said third means is untrue and Vxcex94 greater than Vk is true, or the minimum phase selected by the third means is the same as the single-phase operation phase of the short-circuit distance relay element; and a fifth means that deems valid the operation output of the short-circuit distance relay element, irrespective of the result of the decision of the second means or third means if the operation phase of the short-circuit distance relay element exists for two or more phases.
Another invention consists of a digital distance relay having a short-circuit distance relay element that inputs respectively the voltage and current from an AC power system of three phases a, b and c, calculates a fault impedance from these voltages and currents and compares this with a set impedance and that, depending on the result of this comparison, makes an operation decision in the event of a fault within a transmission line protection zone, comprising: a first means for calculating the amplitudes |Vab|, |Vbc|, and |Vca| of the line-to-line voltages of the three phases; a second means for making a comparison decision of the absolute value (|Vxcex94|=||Vab|xe2x88x92|Vbc||) (rotated in phase order for the other phases) of the phase-to-phase difference of the voltage amplitudes and a sensitivity constant Vk; a third means for making a comparison decision of the phase-to-phase difference (Vxcex94=|Vab|xe2x88x92|Vbc|)(rotated in phase order for the other phases) of the voltage amplitudes and Vk; a fourth means that selects the minimum phase (|Vmin|=min(|Vab|, |Vbc|, |Vca|)) of the absolute values of the line-to-line voltages of the three phases; a fifth means that deems valid the operation output of the short-circuit distance relay element if the phase for which |Vxcex94| less than Vk in said second means and said third means is untrue and Vxcex94 greater than Vk is true, or the minimum phase selected by the fourth means is the same as the single-phase operation phase of the short-circuit distance relay element; and a sixth means that deems valid the operation output of the short-circuit distance relay element, irrespective of the result of the decision of the second means or third means or fourth means if operation phase of the short-circuit distance relay element exists for two or more phases.
Another invention consists in a digital distance relay having a short-circuit distance relay element that inputs respectively the voltage and current from an AC power system of three phases a, b and c, calculates a fault impedance from these voltages and currents and compares this with a set impedance and that, depending on the result of this comparison, makes an operation decision in the event of a fault within a transmission line protection zone, comprising: a first means for calculating the amplitudes |Vab|, |Vbc|, and |Vca| of the line-to-line voltages of the three phases; a second means for making a comparison decision of the absolute value (|Vxcex94|=||Vab|xe2x88x92|Vbc||) (rotated in phase order for the other phases) of the phase-to-phase difference of the voltage amplitudes and a sensitivity constant Vk; a third means for making a comparison decision of the phase-to-phase difference (V66 =|Vab|xe2x88x92|Vab|Vbc|)(rotated in phase order for the other phases) of the voltage amplitudes and the Vk; a fourth means that selects the minimum phase (|Vmin|=min(|Vab|, |Vbc|, |Vca|)) of the absolute values of the line-to-line voltages of the three phases; a fifth means that deems valid the operation output of the short-circuit distance relay element if the phase for which |Vxcex94| less than Vk in the second means and the third means is untrue and Vxcex94 greater than Vk is true, or the minimum phase selected by the fourth means is the same as the single-phase operation phase of the short-circuit distance relay element; and a sixth means that deems valid the operation output of the short-circuit distance relay element, irrespective of the result of the decision of the second means or third means or fourth means if operation phase of the short-circuit distance relay element exists for two or more phases.
Another invention consists in a digital distance relay having a short-circuit distance relay element that inputs respectively the voltage and current from an AC power system of three phases a, b and c, by multiplying the input current by a set impedance, converts this to a voltage amount, calculates the phase difference or absolute value difference with the input voltage as an operation amount and restriction amount, compares the magnitudes of these, and, in accordance with this comparison result, makes an operation decision in the event of a fault within a transmission line protection zone, comprising: a first means for calculating the amplitudes |Vab|, |Vbc|, and |Vca| of the line-to-line voltages of the three phases; a second means for making a comparison decision of the absolute value (|Vxcex94|=||Vab|xe2x88x92|Vbc||) (rotated in phase order for the other phases) of the phase-to-phase difference of the voltage amplitudes and a sensitivity constant Vk; a third means for making a comparison decision of the phase-to-phase difference (Vxcex94=|Vab|xe2x88x92|Vbc|)(rotated in phase order for the other phases) of the voltage amplitudes and Vk; a fourth means that selects the minimum phase (|Vmin|=min(|Vab|, |Vbc|, |Vca|)) of the absolute values of the line-to-line voltages of the three phases; a fifth means that deems valid the operation output of the short-circuit distance relay element if the phase for which |Vxcex94| less than Vk in said second means and said third means is untrue and Vxcex94 greater than Vk is true, or the minimum phase selected by the fourth means is the same as the single-phase operation phase of the short-circuit distance relay element; and a sixth means that deems valid the operation output of the short-circuit distance relay element, irrespective of the result of the decision of the second means or third means or fourth means if operation phase of the short-circuit distance relay element exists for two or more phases.
With immediate mentioned former four inventions, a minimum phase voltage condition is added to the operation decision of the short-circuit distance relay, so unwanted operation due to over-reach of a sound phase element can be prevented, making it possible to achieve stable operation correctly responding to the faulted phase only.
Another invention consists of a digital ground fault distance relay having ground fault distance relay elements that input respectively the voltage and current from an AC power system of three phases a, b and c, calculate a fault impedance from these voltages and currents and compare this with a set impedance and that, depending on the result of this comparison, make an operation decision in the event of a fault within a transmission line protection zone, comprising: a first means that makes an operation decision of an insufficient voltage relay in accordance with a phase voltage; a second means that identifies whether or not the operation result obtained from this first means is present for two or more phases; and a third means that, if the operation phase is present for two or more phases in this second means, performs output control of all of the operation outputs of the ground fault distance relay elements to the non-actuated side.
Another invention consists of a digital ground fault distance relay having a ground fault distance relay element that inputs respectively the voltage and current from an AC power system of three phases a, b and c, calculates a fault impedance from these voltages and currents and compares this with a set impedance and that, depending on the result of this comparison, makes an operation decision in the event of a fault within a transmission line protection zone, and an mho relay element of a third-stage time-limited operation zone, comprising: a first means that identifies whether or not the previous-stage relay unit operation output constituting time-limited operation of the mho relay element is present for two or more phases; and a second means that, if the operation phase is present for two or more phases in this first means, performs output control of the operation decision output of the ground fault distance relay element to the non-actuated side.
Another invention consists in a digital ground fault distance relay having ground fault distance relay elements that input respectively the voltage and current from an AC power system of three phases a, b and c, by multiplying the input current by a set impedance, convert this to a voltage amount, calculate the phase difference or absolute value difference with the input voltage as an operation amount and restriction amount, compare the magnitudes of these, and, in accordance with this comparison result, make an operation decision in the event of a fault within a transmission line protection zone, comprising: a first means that makes an operation decision of an insufficient voltage relay in accordance with a phase voltage; a second means that identifies whether or not the operation result obtained this first means is present for two or more phases; and a third means that, if the operation phase is present for two or more phases in this second means, performs output control of all of the operation outputs of the ground fault distance relay elements to the non-actuated side.
Another invention consists of a digital ground fault distance relay having ground fault distance relay elements that input respectively the voltage and current from an AC power system of three phases a, b and c, by multiplying the input current by a set impedance, convert this to a voltage amount, calculate the phase difference or absolute value difference with the input voltage as an operation amount and restriction amount, compare the magnitudes of these, and, in accordance with this comparison result, make operation decisions in the event of a fault within a transmission line protection zone, and an mho relay element, comprising: a first means that identifies whether or not the previous-stage relay unit operation output constituting time-limited operation of the mho relay element is present for two or more phases; and a second means that, if the operation phase is present for two or more phases in this first means, performs output control of all of the operation decision outputs of the ground fault distance relay elements to the non-actuated side.
With the immediate mentioned former four inventions, the single-phase operation condition of an insufficient voltage relay element or mho relay element is added to the operation decision of the ground fault distance relay, so unwanted operation due to over-reach of a sound phase element can be prevented, making it possible to achieve stable operation correctly responding to the faulted phase only.